The present invention relates to a clad material for ornamental applications and a process for producing the same, and more particularly relates to improvement in production of Ti-core clad material for ornamental applications such as eyeglass frames and watch bands.
Ti has been widely used in the field due to its light weight, high rigidity and rich anti-corrosion. Usually for increased aesthetic effect, a Ti core is plated with Au. Dispite troublesome pretreatment, this Au plating cannot assure sufficient bonding strength because of passivity of the Ti core. Thus, due to easy separation of the Au plate, the plated product is unsuited for use in practice.
As a substitute for such a plated product, a Ti-core clad material was proposed in which a Ti core is covered, through cladding, with Au, Au-base alloy, Pt or Pt-base alloy sheath. In this case, however, a big difference in workability between the core and the sheath tends to mar the surface of the sheath during working, thereby disenabling production of high quality clad materials. In addition, direct contact of Ti with Au or Pt tends to evolve fragile inter-metallic compounds near the border between the core and the sheath at plastic deformation and or heat treatment following cladding, which lowers bonding strength between the core and the sheath and inevitably causes separation of the latter.
Another type Ti-core clad material was also proposed in which Ti core is covered, through cladding, with Ni, Ni-base alloy or Cu-base alloy.
Use of such a sheath assures easy brazing of the clad material. Here again inter-metallic compounds are evolved near the border between the core and sheath due to heat at brazing, which lowers brazing strength of the clad material.
In conventional production of such clad materials, hydrostatic extrusion or explosive bonding has generally been employed for cladding. Such conventional cladding, however, cannot provide the products with sufficient bonding strength. Application of heat concurrently with pressure may achieve ideal cladding but causes the problem of inter-metallic compound production.